Methods and systems disclosed herein relate generally to autonomous sensing of ocean properties, and more specifically to instruments to remotely sense bio-optical properties. A major focus of oceanographic research expected over the next several decades is on the space/time variability of bio-optical processes observed through in situ and remote sensing techniques, and modeling the bio-optical processes. Tools to measure a large suite of optical parameters, in real-time, over long periods, to facilitate algorithm development, relate bio-optical and physical phenomena, and incorporate phenomena into ocean models will be needed. A continuous, long-term record could be needed to resolve the small-to-fine scale spatial and temporal processes operating on the shelf transition zone and in the coastal zone, for example, but not limited to, wind events, sediment re-suspension and transport, tidal effects, long-shore currents, and loop current intrusions.
Currently, physical data and limited optical data, including temperature, salinity, current, wave measurements, backscattering at two wavelengths, and fluorescence at one wavelength can be obtained autonomously. However, current technology either lacks a complete set of optical instrumentation, or it is not trawl-resistant, or both. If the current technology is not trawl-resistant, unattended operation in coastal areas can be risky and could result in damage to the instrumentation.
Pontoon and buoy-based profiling systems that float at the surface and profile downward, as opposed profiling systems that rest on the bottom and profile upward, do not have the capability to accommodate the full suite of optical instrumentation. Furthermore, since floating profiling systems have a continuous surface expression, they are subject to severe wind and wave conditions and ship traffic collisions that could impact operation. Other optical moorings can have physical and optical sensors placed only at the surface or at a few fixed locations along a vertical cable. Thus, although they are able to collect long-term data records, the sensors only sample at a few fixed depths in the water column, and therefore cannot completely resolve the vertical structure.
Vertical profiles collected using standard physical/optical profiling packages lowered by winch from a ship platform have severe sampling limitations. For ship-based collection of data sets, survey work could be required at additional monetary, labor, and opportunity cost. Thus, ship sampling cannot easily replace autonomous sampling to capture a long-term, unattended sampling record.
Current autonomous technology houses scientific instruments that sit on the seafloor and combine an upward looking acoustic Doppler current profiler (ADCP) with an up/down casting float containing a single optical sensor, a conductivity/temperature/depth probe, a pressure sensor for wave data, a pressure sensor for the CTD, and a satellite transceiver. These housings are constructed of fiberglass. Other bio-optical mooring systems use a pump mechanism to circulate water during the measurement, have large power requirements and lack anti-fouling mechanisms, which result in shorter deployment periods.
What is needed is a system for profiling from a bottom mooring, facilitating oceanographic research to address scientific questions regarding the coupling of optical and physical ocean properties, the validity of algorithms that extrapolate surface satellite optical observations to depth, and the variability of optical properties over short time and space scales. What is further needed is a system that accommodates multiple optical sensors that do not require a pump mechanism, anti-fouling mechanisms and miniaturized instruments. Still further, what is needed is a system having relatively low power requirements, relatively long unattended deployment time, and a relatively high sampling frequency with respect to the current technology.